Dynamic Vapor Sorption Mechanics in Recycled Packaging Substrates
Recycled packaging substrates exhibit non-Fickian moisture uptake and severe hysteresis, reducing compressive strength by over 20 percent under cyclic humidity.
GAB Sorption Model
Mathematical Representation
Sorption isotherm models calculate the equilibrium moisture content of a material as a function of relative humidity at a constant temperature. Physicists and food packaging engineers apply the gab sorption model to describe water vapour absorption across a wide range of water activity. This equation improves upon simpler models by accounting for the different properties of water molecules bound directly to the surface versus those in subsequent layers.
Multilayer Analysis
The mathematical formulation utilizes three distinct parameters to fit the experimental data across water activities ranging from zero to nearly one. It models the monomolecular layer of tightly bound water, the multilayer of partially bound water, and the free water in the pores. Adjusting these parameters allows packaging engineers to predict the shelf life of moisture-sensitive food products.
This predictive capability is especially useful when selecting barrier films or coated paperboard for dry food storage. Understanding these curves avoids under-designing the moisture barrier.
Sizing Design
Package sizing requires accurate calculations of the moisture transmission rate to avoid food spoilage during transit. Designers use the model to establish the dry-state limit below which the food remains crisp and free from microbial growth. This step ensures that the barrier material is not over-specified or under-specified for the intended shelf life.